1. Field of Invention
The present invention relates to methods for splitting split type conjugate fibers and artificial leather made by the methods.
2. Related Prior Art
A so-called conjugate fiber includes two or more polymers of different types or two or more polymers of the same type but with different properties. The polymers are spun to form chemical fibers by a conjugate spinning method. In the conjugate spinning method, two different polymers are molten and respectively flow in two channels and then meet at an inlet of a spinneret. The molten polymers are extruded from the spinneret and then solidified into a conjugate fiber. The conjugate fiber is often reeled for later use. According to different positions of the polymers in a cross-sectional view, the conjugate fibers can be classified into a split type (including side by side type and sheath/core type) and a sea-island type. The fibers in a split type conjugate fiber may be separated from one another by a mechanic method or a dissolution method. Alternatively, certain portions of the polymers may be dissolved for the purposes of thinning the fibers.
The fineness of a so-called ultrafine fiber is smaller than 0.3 dtex. Conventionally, to make artificial leather from the ultrafine fibers, a non-woven fabric (or “substrate”) made from conjugate fibers is submerged in a resin. The conjugate fibers of the substrate are dissolving so as to provide a semi-product of the artificial leather including ultrafine fibers each with a fineness smaller than 0.3 dtex. Finally, a superficial layer is adhered to the semi-product of the artificial leather to provide the final product of the artificial leather. This artificial leather includes a microstructure like that of real leather and is soft, light and excellent in drape. However, a lot of solvent or alkali solution is used in the dissolution step of the conjugate fibers.
For example, Taiwanese Patent Publication No. 101199 discloses a method for making ultrafine fibers and fabrics of the same. Each of the fibers is coated with a film of polyester. The films of polyester are dissolved in an alkali solution before the fibers are mechanically split. However, toxic waste is produced as a result of the dissolving of the films of polyester by the alkali solution, leading to grave pollution of water. The alkali solution that dissolves the films of polyester can be recycled; however, the cost is inevitably increased.
Taiwanese Patent Publication No. 252156 discloses a method for splitting conjugate fibers. Each of the conjugate fibers includes polymers arranged like the segments of an orange based on their different crystallization. The speed of reeling during spinning is increased to 3000-8000 m/min. The increased speed of reeling stretches and tears and therefore splits the fibers. However, when the number of the segments is large, the splitting result of the fibers is poor due to incomplete tearing or breakage of some of the fibers.
Taiwanese Patent Publication No. 179714 discloses a method for splitting conjugate fibers and fabrics of the same. Each of the conjugate fibers includes polymers of polyamide and polyester arranged like the segments of an orange. However, because the two polymers adhere to each other well, benzyl alcohol, caustic sodium or an acid solvent must be used to dissolve the polyamide or polyester so as to split the fibers, and hence causes serious pollution of water.
Taiwanese Patent Publication No. 202489 discloses a method for splitting fibers and a method for dying the same. An acid solvent is used to dissolve polyamide so as to obtain ultrafine fibers of polyester. Produced in the method is waste that cannot easily be handled.
Japanese Patent Publication 1993-331758 discloses production of ultrafine fiber. A conjugate fiber is made of two polymers that properly adhere to each other so that they are not separated from each other during combing and needle punch and that they are separated from each other for their different degrees of contraction in boiling hot water during mechanical splitting. However, it has proven to be inadequate when the number of splitting is large.
Japanese Patent Publication 1993-051820 discloses conjugate fiber that can be split. The conjugate fiber includes a plurality of parts made of PET that is modified so that it can easily be dissolving. The parts are in parallel to each other. Thus, the conjugate fiber can easily be split. However, PET must be dissolved by an alkali solvent such as caustic sodium during splitting. Therefore, there is serious pollution of water.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.